Electric machines, such as electric motors and/or electric generators, are used in energy conversion. In the aircraft industry, it is common to find an electric motor having a combination of motor and generator modes, where the electric machine, in motor mode, is used to start an aircraft engine, and, depending on the mode, functions as a generator, too, to supply electrical power to the aircraft systems. Regardless of the mode, the machines typically include a rotor having main windings that are driven to rotate by a source of rotation, such as a mechanical or electrical machine, which for some aircraft may be a gas turbine engine.